Rydon/RMC does make good stuff, but...
I really must say that I didn't get a run-around about returning the offending nipples, just that I was told more than once that they were "..designed to use #10 caps..." . A strange aspect of this whole story is that the place that I originally found the nipples for sale had the product advertised as made to use #11 caps.
How I really wished they would have worked with any caps at all, but as I stated earlier I tried every type commonly available, and they just wouldn't hold any caps at all, so I was issued a return authorization number that resulted in a refund of the shipping costs I incurred from the order to begin with, which was highly unusual, but a welcome attempt by the seller to mend fences.
By the way, I really liked the Rydon/RMC hardened nipple wrench that was recommended by mykeal in the first response to this thread.
It was first rate stuff at a very fair price, which should go to show you that the manufacturer does produce quality products, it's just that the nipples in question didn't "cut the mustard".
I wouldn't be fearful of trying other products from them in the future, but I did learn a lesson about aftermarket replacement nipples in general.